This invention relates to a vacuum valve, and more particularly to a two-stage vacuum valve such as for use in a vacuum packaging apparatus and method.
A vacuum packaging machine typically includes a series of vacuum heads or chambers that are selectively positioned so as to enclose a package to be evacuated and sealed. Each vacuum head is typically moved into engagement with a package support, which may be in the form of a plate, which supports the package. The plate defines a flat engagement surface, and the vacuum head engages the engagement surface of the plate, and defines an interior within which the package is located. Vacuum is then supplied to the interior of the vacuum head, by operation of a vacuum source that is connected to the vacuum head through a vacuum conduit. The vacuum supplied to the interior of the vacuum head evacuates the package, and the package is then sealed so at to close the evacuated package. The vacuum head is then disengaged from the engagement surface and the sealed package is discharged from the plate.
In prior art vacuum packaging machines, vacuum is supplied to the interior of the vacuum head or chamber by operation of a vacuum valve that is interposed between the vacuum source and the vacuum head or chamber. The valve includes a single poppet member that controls the supply of vacuum to the interior of the vacuum head. When the poppet member is open, vacuum is supplied to the interior of the vacuum head. When the poppet member is closed, the supply of vacuum to the interior of the vacuum head is cut off and the interior of the vacuum head is vented, i.e. exposed to ambient air pressure. With this arrangement, the vacuum valve is either in an evacuation mode or a venting mode, and evacuation and venting of the vacuum head cannot be controlled separately from each other.
It is an object of the present invention to provide a vacuum control valve, such as for use in a vacuum packaging machine, in which the evacuation and venting functions can be controlled separately from each other, to enable precise control over the timing of the evacuation and venting functions. It is a further object of the present invention to provide such a vacuum control valve which has a compact and efficient design that simplifies the components and assembly of the valve, so as to minimize the cost of the valve while providing the significant advantages that can be attained by separating control over the evacuation and venting functions. Yet another object of the invention is to provide such a vacuum valve that is well suited for mounting to a vacuum manifold that also functions as a support for the vacuum head to which the vacuum valve is connected, and that moves along with the vacuum head toward and away from the package to be evacuated.
In accordance with the present invention, a vacuum control valve for a vacuum packaging system, which includes a vacuum chamber and a vacuum source, includes a valve body defining a cavity, an inlet opening and a vent opening. A vacuum supply control member is movably mounted to the valve body at the inlet opening, and is movable between an open position in which the vacuum supply control member opens the inlet opening, and a closed position in which the vacuum supply control member closes the inlet opening. A vent or exhaust control member is movably mounted to the valve body at the vent opening, and is movable between an open position in which the vent control member opens the vent opening, and a closed position in which the vent control member closes the vent opening. The vacuum supply control member and the vent control member are movable between the open and closed positions independently of each other, for selectively controlling the supply of vacuum through the valve body cavity when the vacuum supply control member is in the open position and the vent control member is in the closed position, and for selectively venting vacuum through the valve body cavity when the vacuum supply control member is in the closed position and the vent control member is in the open position. In one form, the vent opening and the inlet opening are in alignment with each other, and the vent control member and the vacuum supply control member are mounted to the valve body for movement along a common longitudinal axis between the open and closed positions. The vent control member and the vacuum supply control member may be mounted to the valve body for coaxial movement between the open and closed positions.
The valve may be formed so as to include an actuator section, and the vent control member and the vacuum supply control member each includes a piston-type actuator movably mounted to the actuator section for controlling movement of the vent control member and the vacuum supply control member between the open and closed positions. The vent opening may be in communication with the valve body cavity and the exterior of the valve body by means of a vent passage located between the valve body cavity and the actuator section. The piston-type actuators are interconnected with the control members by means of actuator rods that extend from the actuator section and through the vent passage for connection to the control members. The vent control member may be in the form of a poppet member that is normally in the closed position over the vent opening, and the vacuum supply control member may be in the form of a poppet member that is normally in the closed position over the inlet opening.
The invention also contemplates a vacuum packaging system that includes a vacuum source, one or more evacuation chambers and a vacuum control valve substantially in accordance with the foregoing summary, as well as a method of selectively evacuating and venting a vacuum chamber, also substantially in accordance with the foregoing summary.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.